Synchronizing Operations Among a Plurality of Independently Clocked Digital Data Processing Devices

ABSTRACT

Example systems, apparatus, and methods receive audio information including a plurality of frames from a source device, wherein each frame of the plurality of frames includes one or more audio samples and a time stamp indicating when to play the one or more audio samples of the respective frame. In an example, the time stamp is updated for each of the plurality of frames using a time differential value determined between clock information received from the source device and clock information associated with the device. The updated time stamp is stored for each of the plurality of frames, and the audio information is output based on the plurality of frames and associated updated time stamps. A number of samples per frame to be output is adjusted based on a comparison between the updated time stamp for the frame and a predicted time value for play back of the frame.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. application Ser. No.15/081,911 filed Mar. 27, 2016, and currently pending; U.S. applicationSer. No. 15/081,911 is a continuation of U.S. application Ser. No.14/564,544, filed Dec. 9, 2014, and issued on May 24, 2016, as U.S. Pat.No. 9,348,354; U.S. application Ser. No. 14/564,544 is a continuation ofU.S. application Ser. No. 14/176,808, filed on Feb. 10, 2014, and issuedon Jan. 20, 2015, as U.S. Pat. No. 8,938,637; U.S. application Ser. No.14/176,808 is a continuation of U.S. application Ser. No. 13/724,048,filed on Dec. 21, 2012, and issued on Apr. 1, 2014, as U.S. Pat. No.8,689,036; U.S. application Ser. No. 13/724,048 is a continuation ofU.S. application Ser. No. 13/204,511, filed on Aug. 5, 2011, and issuedon Feb. 5, 2013, as U.S. Pat. No. 8,370,678; U.S. application Ser. No.13/204,511 is a continuation of U.S. application Ser. No. 11/801,468,filed on May 9, 2007, and issued on Sep. 13, 2011, as U.S. Pat. No.8,020,023; U.S. application Ser. No. 11/801,468 is acontinuation-in-part of U.S. application Ser. No. 10/816,217 filed onApr. 1, 2004, and issued on Jul. 31, 2012, as U.S. Pat. No. 8,234,395,and claims priority to U.S. Provisional App. No. 60/860,964 filed onNov. 22, 2006, and U.S. Provisional App. No. 60/876,455 filed on Dec.20, 2006; U.S. application Ser. No. 10/816,217 claims priority to U.S.Provisional App. 60/490,768 filed on Jul. 28, 2003. The entire contentsof application Ser. Nos. 14/564,544; 14/176,808; 13/724,048; 13/204,511;11/801,468; 10/816,217; 60/860,964; 60/876,455; and 60/490,768 areincorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates generally to digital content, and moreparticularly, to systems and methods for synchronizing operations amonga plurality of independently clocked digital data processing deviceswithout a voltage controlled crystal oscillator.

DESCRIPTION OF RELATED ART

Conventionally, playing the same digital content over multiple audioand/or audiovisual reproduction devices simultaneously or in synchronyis limited by the inherent differences in the frequencies or clock ratesof the crystal oscillators influencing the rates in which the digitalcontent is converted to analog content for playing over the respectiveaudio and/or audiovisual reproduction devices. Previous approaches thatsolve this problem require expensive hardware and/or circuitry, whichalso requires additional space within the audio and/or audiovisualreproduction device. There is thus a need for systems and methods forsynchronizing operations among a plurality of independently clockeddigital data processing devices without a voltage controlled crystaloscillator.

SUMMARY OF THE INVENTION

Exemplary systems and methods are provided that include a distributiondevice that maintains a clock rate and distributes a series of tasks toa group of execution devices (or synchrony group). Each task has aplurality of samples per frame associated with a time stamp indicatingwhen the task is to be executed. An execution device executes the seriesof tasks at the times indicated and adjusts the number of samples perframe in relation to the clock rate maintained by the distributiondevice. The synchrony group may also be configured to adjust samples perframe in relation to a clock rate maintained by the distribution device.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an exemplary networked system;

FIG. 2 illustrates a functional block diagram of a synchrony grouputilizing a plurality of zone players formed within the exemplarynetworked system depicted in FIG. 1;

FIG. 3 illustrates a functional block diagram of a zone player for usein the networked system depicted in FIG. 1; and

FIG. 4 illustrates an exemplary digital framing methodology.

DETAILED DESCRIPTION

Referring to FIG. 1, an exemplary network audio system 10 is shown inwhich various embodiments of the invention may be practiced. Althoughthe term “audio” is used in connection with the exemplary network audiosystem 10, it will readily be appreciated that the herein describedsystems and methods may be employed with other forms of digital data,including visual and/or audiovisual digital data.

The exemplary network audio system 10 includes at least one zone player11, interconnected by a local network 12, all of which may operate underthe control of one or more user interface modules identified byreference numeral 13. The zone player 11 is sometimes referred to as adigital data processing device. One or more of the zone players 11 mayalso be connected to one or more audio information sources, which willgenerally be identified herein by reference numeral 14, and/or connectedto one or more audio reproduction devices, which will generally beidentified by reference numeral 15. It will be appreciated that thenumber of audio information sources may vary as among the various zoneplayers 11, and some zone players may not have any audio informationsources connected thereto.

A plurality of zone players 11 associated with a network audio system 10may be distributed throughout an establishment, such as residence, anoffice complex, a hotel, a conference hall, an amphitheater, auditorium,or other types of establishments as will be apparent to those skilled inthe art. For example, a zone player 11 and its associated audioinformation source(s) and audio reproduction device(s) may be located ina living room, another zone player may be located in a kitchen, anotherzone player may be located in a dining room, and other'zone players maybe located in bedrooms, to selectively provide entertainment in thoserooms. The audio information sources 14 may be any of a number of typesof conventional sources of audio information, including, for example,compact disc (“CD”) players, AM and/or FM radio receivers, analog ordigital tape cassette players, analog record turntables and the like. Inaddition, the audio information sources 14 may comprise digital audiofiles stored locally on, for example, personal computers (PCs), personaldigital assistants (PDAs), or similar devices capable of storing digitalinformation in volatile or non-volatile form. The audio informationsources 14 may also comprise an interface to a wide area network such asthe Internet, or any other source of audio information, or an interfaceto radio services delivered over, for example, satellite. Audioinformation obtained over the wide area network may comprise, forexample, streaming digital audio information such as Internet radio,digital audio files stored on servers, and other types of audioinformation and sources as will be appreciated by those skilled in theart.

Generally, the audio information sources 14 provide audio informationassociated with audio programs to the zone players for playback. A zoneplayer that receives audio information from an audio information source14 that is connected thereto may provide playback and/or forward theaudio information, along with playback timing information, over thelocal network 12 to other zone players for playback. Users, using userinterface module 13, may also enable different groupings or sets of zoneplayers to provide audio playback of different audio programssynchronously.

Referring to FIG. 2, an exemplary group of execution devices (or“synchrony group”) 20 according to one embodiment of the invention isshown. The exemplary synchrony group 20 comprises synchrony group memberdevices or member devices including a master execution device 21 andzero or more slave devices 22(1) through 22(G) (generally identified byreference numeral 22(g)), all of which synchronously play an audioprogram provided by an audio information channel device 23. The audioinformation channel device 23 is sometimes referred to as a task sourceor a task distribution device. Each master execution device 21, slavedevice 22(g), and/or audio information channel device 23 may utilize azone player 11 as depicted in FIG. 1. The zone player 11 may function asan audio information channel device 23, a master execution device 21, ora slave device 22(g) for the synchrony group 20. The audio informationchannel device 23 may obtain audio information for the audio programfrom an audio information source 14, add playback timing information,and transmit the combined audio and playback timing information to themaster execution device 21 and slave devices 22(g) over local network 12(FIG. 1) for playback. The playback timing information that is providedwith the audio information, together with clock timing informationprovided by the audio information channel device 23 to the variousdevices 21 and 22(g), enables the master execution device 21 and slavedevices 22(g) of the synchrony group 20 to play the audio informationsimultaneously.

The master execution device 21 and the slave devices 22(g) receive theaudio and playback timing information, as well as the clock timinginformation, that are provided by the audio information channel device23, and play back the audio program defined by the audio information.The master execution device 21 also communicates with the user interfacemodule 13, controls the operations of the slave devices 22(g) in thesynchrony group 20, and controls the operations of the audio informationchannel device 23 that provides the audio and playback timinginformation for the synchrony group 20. Generally, the initial masterexecution device 21 for the synchrony group will be the first zoneplayer 11 that a user wishes to play an audio program. However, themaster execution device 21 may be migrated from a first zone player to asecond zone player, which preferably will be a zone player that iscurrently operating as a slave device 22(g) in the synchrony group.

In addition, under certain circumstances, the audio information channeldevice 23 may be migrated from one zone player to another zone player,which also may be a zone player that is currently operating as a memberof the synchrony group 20. It will be appreciated that the zone playerthat operates as the master execution device 21 may be migrated toanother zone player independently of the migration of the audioinformation channel device 23. For example, if a first zone player isoperating as both the master execution device 21 and the audioinformation channel device 23 for a synchrony group 20, the function ofthe master execution device 21 may be migrated to a second zone playerwhile the first zone player is still operating as the audio informationchannel device 23. Similarly, if a first zone player is operating asboth the master execution device 21 and the audio information channeldevice 23 for a synchrony group 20, the source function of the audioinformation channel device 23 may be migrated to a second zone playerwhile the first zone player is still operating as the master executiondevice 21. In addition, if a first zone player is operating as both themaster execution device 21 and the audio information channel device 23for a synchrony group 20, the master execution device 21 may be migratedto a second zone player and the audio information channel device may bemigrated to a third zone player.

The master execution device 21 receives control information from theuser interface module 13 for controlling the synchrony group 20 andprovides status information indicating the operational status of thesynchrony group 20 to the user interface module 13. Generally, thecontrol information from the user interface module 13 causes the masterexecution device 21 to enable the audio information channel device 23 toprovide audio and playback timing information to the synchrony group,allowing the devices 21 and 22(g) that are members of the synchronygroup 20 to play the audio program synchronously. In addition, thecontrol information from the user interface module 13 causes the masterexecution device 21 to enable other zone players to join the synchronygroup as slave devices 22(g) and/or to cause slave devices 22(g) todisengage from the synchrony group. Control information from the userinterface module 13 may also cause the zone player 11 that is currentlyoperating as the master execution device 21 to disengage from thesynchrony group, but prior to doing so, that zone player will cause thefunction of the master execution device 21 to transfer from that zoneplayer 11 to a second zone player, preferably to a second zone playerthat is currently a slave device 22(g) in the synchrony group 20. Thecontrol information from the user interface module 13 may also cause themaster execution device 21 to adjust its playback volume and/or toenable individual ones of the various slave devices 22(g) to adjusttheir playback volumes. In addition, the control information from theuser interface module 13 may cause the synchrony group 20 to terminateplaying of a current track of the audio program and skip to the nexttrack, and to re-order tracks in a play list of tracks defining theaudio program that are to be played by the synchrony group 20. Thestatus information that the master execution device 21 may provide tothe user interface module 13 may include such information as a name orother identifier for the track of an audio work that is currently beingplayed, the names or other identifiers for upcoming tracks, theidentifier of the zone player 11 that is currently operating as themaster execution device 21, and identifiers of the zone players that arecurrently operating as slave devices 22(g). In one embodiment, the userinterface module 13 may include a display that can display the statusinformation to the user. It will be appreciated that the zone player 11that is operating as the audio information channel device 23 for onesynchrony group may also comprise the master execution device 21 or anyof the slave devices 22(g) in another synchrony group. This may occurif, for example, the audio information source that is to provide theaudio information that is to be played by the one synchrony group isconnected to a zone player also being utilized as the master executiondevice or a slave device for the other synchrony group.

Referring to FIG. 3, a functional block diagram of an exemplary zoneplayer 11 constructed in accordance with one embodiment of the inventionis shown. The exemplary zone player 11 includes an audio informationsource interface 30, an audio information buffer 31, a playbackscheduler 32, a digital to analog converter 33, an audio amplifier 35,an audio reproduction device interface 36, a network communicationsmanager 40, a network interface 41, and a control module 42. In analternative system and method, the exemplary zone player 11 may notinclude the audio amplifier 35. In a further embodiment, the zone player11 includes and/or forms part of the audio reproduction device 15. Thezone player 11 also has a device clock 43 that provides timing signalsthat control the general operations of the zone player 11. In addition,the zone player 11 includes a user interface module interface 44 thatcan receive control signals from the user interface module 13 (FIGS. 1and 2) for controlling operations of the zone player 11, and providesstatus information to the user interface module 13.

Generally, the audio information buffer 31 buffers audio information, indigital form, along with playback timing information. If the zone player11 is operating as the audio information channel device 23 (FIG. 2) fora synchrony group 20, the information that is buffered in the audioinformation buffer 31 may include the audio and playback timinginformation that will be provided to the devices 21 and 22(g) in thesynchrony group 20. If the zone player 11 is operating as the masterexecution device 21 or a slave device 22(g) for a synchrony group (20),the information that is buffered in the audio information buffer 31 mayinclude the audio and playback timing information that the zone player11 is to play. The audio information buffer 31 may receive audio andplayback timing information from two sources, namely, the audioinformation source interface 30 and the network communications manager40. In particular, if the zone player 11 is operating as the audioinformation channel device 23 for a synchrony group 20, and if the audioinformation source is a source 14 connected to the zone player 11, theaudio information buffer 31 may receive and buffer audio and playbacktiming information from the audio information source interface 30.Alternatively, if the zone player 11 is operating as the audioinformation channel device 23 for a synchrony group 20, and if the audioinformation source is a source 14 connected to the network 12, or asource available over a wide area network, the audio information buffer31 may receive and buffer audio and playback timing information from thenetwork communications manager 40. However, if the zone player 11 isoperating as the master execution device 21 or a slave device 22(g) in asynchrony group 20, and if the zone player 11 is not also the audioinformation channel device 23 providing audio and playback timinginformation for the synchrony group 20, the audio information buffer 31may receive and buffer audio and playback timing information from thenetwork communications manager 40. It will be appreciated that, if thezone player 11 is not a member of the synchrony group, the zone player11 may not play this buffered audio and playback timing information.

According to some embodiments, the audio information source interface 30connects to the audio information source(s) 14 associated with the zoneplayer 11. While the zone player 11 is operating as the audioinformation channel device 23 for a synchrony group 20, and if the audioinformation is to be provided by a source 14 connected to the zoneplayer 11, the audio information source interface 30 will selectivelyreceive audio information from one of the audio information source(s) 14to which the zone player is connected and store the audio information inthe audio information buffer 21. If the audio information from theselected audio information source 14 is in analog form, the audioinformation source interface 30 will convert it to digital form. Theselection of the audio information source 14 from which the audioinformation source interface 30 receives audio information is under thecontrol of the control module 42, which, in turn, receives controlinformation from the user interface module through the user interfacemodule interface 44. The audio information source interface 30 addsplayback timing information to the digital audio information and buffersthe combined audio and playback timing information in the audioinformation buffer 21. More specifically, the audio information sourceinterface 30 receives audio information from an audio information source14, converts it to digital form if necessary, and buffers it along withplayback timing information in the audio information buffer 21. Inaddition, the audio information source interface 30 may also provideformatting and scheduling information for the digital audio information,whether as received from the selected audio information source 14 or asconverted from an analog audio information source. The formatting andscheduling information will control not only playback by the zone player11 itself, but will also enable other zone players that may be in asynchrony group for which the zone player 11 is the master executiondevice to play the audio program associated with the audio informationin synchrony with the zone player 11.

In one particular embodiment, the audio information source interface 30divides the audio information associated with an audio work into aseries of frames, with each frame comprising digital audio informationfor a predetermined period of time. As used herein, an audio track maycomprise any unit of audio information that is to be played withoutinterruption, or a series of one or more audio tracks that are to beplayed in succession. It will be appreciated that the tracks comprisingthe audio program may also be played without interruption, oralternatively playback between tracks may be interrupted by a selectedtime interval.

FIG. 4 depicts an illustrative framing strategy used in connection withone system and method of the invention for a digital audio streamcomprising an audio work. A framed digital audio stream 50 comprises asequence of frames 51(1) through 51(F) (generally identified byreference numeral 51(f)). Here, “(f)” may represent a generic sequencenumber for any particular frame (51), with the actual sequence numbersranging from “( 1 )” to “(F).” Each frame 51(f), in turn, comprises aseries of audio samples 52(f)(1) through 52(f)(S) (generally identifiedby reference numeral 52(f)(s)) of the audio track. The number of audiosamples 52(f)(s) may differ in each frame 51(f). Associated with eachframe 51(f) is a header 55(f) that includes a number of fields forstoring other information that is useful in controlling playback of theaudio samples in the respective frame 51(f). In particular, the header55(f) associated with a frame 51(f) includes a frame sequence numberfield 56, an encoding type field 57, a sampling rate information field58, a time stamp field 60, an end of track flag 61, and a length flagfield 62. The header 55(f) may also include fields for storing otherinformation that is useful in controlling playback.

Generally, the frame sequence number field 56 receives a number whichwill generically be the number “f,” from the range 1 through F as above,that identifies the relative position of the frame 51(f) in the sequenceof frames containing the digital audio stream 50. The encoding typefield 57 receives a value that identifies the type of encoding and/orcompression that has been used in generating the digital audio stream.Conventional encoding or compression schemes include, for example, MP3and WAV encoding and/or compression schemes, although it will beappreciated that other schemes may be provided for as well. The samplingrate information field 58 includes sampling rate information that mayindicate the sampling rate relative to the audio information channeldevice 23 and/or the sampling rate relative to a current inherent, clockrate of a synchrony group member. The condition of the end of work flag61 indicates whether the frame 51(f) contains the last digital audiosamples for the audio track associated with the framed digital audiowork 50. If the frame 51(f) does not contain the audio samples that areassociated with the end of the digital audio stream 50 for a respectiveaudio work, the end of work flag will be clear. On the other hand, ifthe frame 51(f) does contain the audio samples that are associated withthe end of the digital audio stream 50 for a respective audio work, theend of work flag 61 will be set. In addition, the length flag field 62will contain a value that identifies the number of audio samples in thelast frame 51(F) of the audio work 50. The time stamp field 60 stores atime stamp that identifies the time at which the zone player 11 is toplay the respective frame.

Within each synchrony group member, for each frame of a framed digitalaudio stream 50 that is buffered in the audio information buffer 21, theaudio information source interface 30, using timing information from thedigital to analog converter clock 34, may determine a time at which thezone player 11 is to play the respective frame, and will store a timestamp identifying the playback time in the time stamp field 60. The timestamp associated with each frame is used by the playback scheduler 32 todetermine when the portion of the digital audio stream stored in theframe is to be coupled to the digital to analog converter 33 to initiateplay back. It will be appreciated that the time stamps that areassociated with each of the frames in sequential frames will be suchthat they will be played back in order, and without an interruptionbetween the sequential frames comprising the digital audio stream 50. Itwill further be appreciated that, after a time stamp has been determinedfor the first frame and stored in frame 51(1) of a digital audio stream50, the audio information source interface 30 may determine time stampsfor the subsequent frames in relation to the number of samples in therespective frames and the current inherent clock rate of the synchronygroup member. The time stamps will also preferably be such that frameswill be played back after some slight time delay after they have beenbuffered in the audio information buffer 21.

In some embodiments, the zone players 11 are provided with a digital toanalog converter clock 34 whose time may be set by an element such asthe network communications manager 40. When a zone player 11 isoperating as a member of a synchrony group 20, its networkcommunications manager 40 may use the various types of timinginformation that it receives from the audio information channel device23 to adjust the time value of the synchrony group member's digital toanalog converter clock 34. If the clock's time value is to be adjusted,when the synchrony group member's network communications manager 40initially receives the current time information from the audioinformation channel device 23 for the synchrony group 20, the networkcommunications manager 40 may set the synchrony group member's digitalto analog converter clock 34 to the current time value as indicated bythe audio information channel device's current time information 23. Thenetwork communications manager 40 may set the digital to analogconverter clock 34 to the current time value indicated by the audioinformation channel device's current time information once, orperiodically as it receives the current time information.

After the network communications manager 40 receives a frame 51(f) fromthe network interface 41, it may also obtain, from the digital to analogconverter clock 34, the zone player 11's current time as indicated byits digital to analog converter clock 34. The network communicationsmanager 40 may determine a time differential value that is thedifference between the slave device's current clock time, as indicatedby its digital to analog converter clock 34, and the audio informationchannel device's time as indicated by the audio information channeldevice's clock timing information. Accordingly, if the slave device'scurrent time has a value TS and the audio information channel device'scurrent time, as indicated by the clock timing information, has a valueTC, the time differential value ΔT=TS−TC. If the current time of theslave device in the synchrony group 20, as indicated by its digital toanalog converter clock 34, is ahead of the audio information channeldevice's clock time, the time differential value will have a positivevalue. On the other hand, if the slave device's current time is behindthe audio information channel device's clock time, the time differentialvalue ΔT will have a negative value. If the zone player 11 obtains clocktiming information from the audio information channel device 23periodically while it is a member of the synchrony group 20, the networkcommunications manager 40 may generate an updated value for the timedifferential value ΔT when it receives the clock timing information fromthe audio information channel device 23, and may subsequently use theupdated time differential value.

The network communications manager 40 may use the time differentialvalue ΔT that it generates from the audio information channel devicetiming information and zone player 11's current time to update the timestamps that will be associated with the digital audio information framesthat the zone player 11 receives from the audio information channeldevice. For each digital audio information frame that is received fromthe audio information channel device, instead of storing the time stampthat is associated with the frame as received in the message in theaudio information buffer 21, the network communications manager 40 willstore the updated time stamp with the digital audio information frame.The updated time stamp is generated in a manner so that, when the zoneplayer 11, as a member of the synchrony group plays back the digitalaudio information frame, it will do so in synchrony with other devicesin the synchrony group.

The network communications manager 40 may utilize the updated timestamps associated with respective frames 51(f) to accommodate thecurrent inherent clock rate of the digital to analog converter clock 34of the synchrony group member. For example, when the synchrony groupmember's network communications manager 40 receives a first frame 51(1)having a time stamp having a time value T, it can generate an updatedtime value TU, and store the frame 51(1) with the updated time value TUin the audio information buffer 31 (e.g., 51(1)TU). In addition, sinceboth the number of samples in a frame and the current inherent clockrate of the digital to analog converter clock 34, which determines therate at which the samples in a frame are to be played by the synchronygroup member, are known to the network communications manager 40, thenetwork communications manager 40 can use that information, along withthe time value TU to generate an expected or predicted time value TE forthe time stamp of the next frame 51(2). After the synchrony groupmember's network communications manager 40 receives frame 51(2), it cangenerate the updated time value TU for frame 51(2) and compare that timevalue to the time value TE that was predicted for frame 51(2). If thetwo time values do not correspond, or if the difference between them isabove a selected threshold level, the clock that is used by the audioinformation channel device 23 to generate the time stamps is advancingat a different rate than the synchrony group member's digital to analogconverter clock 34, and the network communications manager 40 may adjustthe number of samples per frame to accommodate the current inherentclock rate of the digital to analog converter clock 34 of the synchronygroup member. If the two time values do correspond (e.g.,51(2)TE=51(2)TU), or the difference is below a threshold level, the timedifferential value is constant, and the network communications manager40 need not accommodate the current inherent clock rate of the digitalto analog converter clock 34 of the synchrony group member.

As an example of one way the network communications manager 40 adjuststhe number of samples in one or more frames to accommodate the currentinherent clock rate of the digital to analog converter clock 34 of asynchrony group member, consider a situation where the clock used by anaudio information channel device 23 indicates a sampling rate of 44105samples per second for the audio information channel device 23. Asynchrony group member with a digital to analog converter clock 34operating at a current inherent clock rate of 44100 samples per secondwill require the network communications manager 40 for the synchronygroup member to reduce the number of samples in one or more frames byfive samples for each one second interval that a particular track(s)comprising one or more frames are being played by the synchrony groupmember.

Continuing this example, a second synchrony group member with a digitalto analog converter clock 34 operating at a current inherent clock rateof 44110 samples per second will require the network communicationsmanager 40 for the second synchrony group member to increase the numberof samples in one or more frames by five samples for each one secondinterval that a particular track(s) comprising one or more frames isbeing played by the second synchrony group member. As a result of theindependent adjustments taking place within the first and secondsynchrony group members in relation to their shared audio informationchannel device 23, both synchrony group members will be playing the sameor nearly the same frame at the same time, despite the differences intheir respective current inherent clock rates.

An information channel device 23 may be configured to periodicallyreceive the respective current inherent clock rates of one or moresynchrony group members comprising a synchrony group. Using thisinformation, the audio information channel device 23 performs therequisite adjustments (instead of the respective one or more synchronygroup members) and sends one or more tracks to each synchrony groupmember, wherein the one or more tracks are adjusted to accommodate thecurrent inherent clock rates of the respective synchrony group members.Accordingly, as a result of the multiple adjustments taking place withinthe audio information channel device 23 with respect to the currentinherent clock rates of the one or more synchrony group members, allsynchrony group members may play the same or nearly the same frame atthe same time, despite the differences in their respective currentinherent clock rates.

The exemplary zone player 11 serving as a synchrony group member may ormay not include an audio amplifier 35 (FIG. 3). Further, as describedherein, an audio information channel device 23 may perform the requisitesample adjustments or each synchrony group member may perform therequisite sample adjustments. Provided the synchrony group member and/orthe audio reproduction device 15 (that is wired or wirelessly associatedwith the synchrony group member) includes at least one amplifier,regardless of scenario, the audio reproduction device 15 may adapt andmaintain as constant a current inherent clock rate of the synchronygroup member. Accordingly, the audio reproduction device 15 may play thesame or nearly the same frame at the same time as another synchronygroup member. This may be advantageous, because some audio reproductiondevices 15 may be incapable of making timely clock rate adjustments.Consequently, by adjusting samples per frame, some exemplary systems andmethods as described herein may function with audio reproduction devices15 that would otherwise be incompatible with those systems and methodsthat include clock rate adjustments for achieving a synchronousperformance.

While various systems and methods have been described above, it shouldbe understood that they have been presented by way of example only, andnot limitation. Thus, the breadth and scope of a preferred embodimentshould not be limited by any of the above-described exemplary systemsand methods.

What is claimed is:
 1. A first zone player comprising: a networkinterface that is configured to provide an interconnection with at leastone data network; a local clock that provides a clock time of the firstzone player; at least one processor; a tangible, non-transitorycomputer-readable medium; and program instructions stored on thetangible, non-transitory computer-readable medium that, when executed bythe at least one processor, cause the first zone player to performfunctions comprising: operating as a standalone zone player that isconfigured to play back audio individually rather than in synchrony withanother zone player; while operating as a standalone zone player,receiving a request to enter into a synchrony group with at least asecond zone player that is communicatively coupled with the first zoneplayer over a local area network (LAN), wherein the second zone playercomprises its own respective local clock that provides a respectiveclock time of the second zone player; in response to receiving therequest to enter into the synchrony group, entering into the synchronygroup with the second zone player and transitioning from operating as astandalone zone player to operating as a slave zone player of thesynchrony group that is configured to play back audio in synchrony withthe second zone player; while operating as the slave zone player of thesynchrony group: receiving, from the second zone player over the LAN,clock information that provides an indication of the clock time of thelocal clock of the second zone player; based on the received clockinformation, determining a differential between the clock time of thelocal clock of the first zone player and the clock time of the localclock of the second zone player; receiving, from the second zone playerover the LAN, (a) audio information for at least a first audio track and(b) playback timing information associated with the audio informationfor the first audio track that comprises an indicator of a first futuretime, relative to the clock time of the local clock of the second zoneplayer, at which the first and second zone players are to begin playingback the audio information for the first audio track in synchrony;updating the first future time to account for the determineddifferential between the clock time of the local clock of the first zoneplayer and the clock time of the local clock of the second zone player;adjusting a sample rate of at least a portion of the audio informationfor the first audio track to compensate for a difference between a clockrate of the local clock of the first zone player and a clock rate of thesecond zone player; and when the clock time of the first zone playerreaches the updated first future time, beginning to play back the audioinformation for the first audio track in synchrony with the second zoneplayer.
 2. The first zone player of claim 1, wherein adjusting thesample rate of at least the portion of the audio information for thefirst audio track to compensate for the difference between the clockrate of the local clock of the first zone player and the clock rate ofthe second zone player comprises: modifying at least a portion of theaudio information for the first audio track to either increase ordecrease a number of audio samples per second included in the portion ofthe audio information.
 3. The first zone player of claim 1, whereinadjusting the sample rate of at least the portion of the audioinformation for the first audio track to compensate for the differencebetween the clock rate of the local clock of the first zone player andthe clock rate of the second zone player comprises: determining anexpected playback time of a given set of one or more audio sampleswithin the audio information for the first audio track; comparing theexpected playback time of the given set of one or more audio sampleswithin the audio information for the first audio track to a futureplayback time of the given set of one or more audio samples as indicatedby the playback timing information received from the second zone playerand thereby determining that there is a difference between the expectedplayback time and the future playback time of the given set of one ormore audio samples that is indicative of the difference between theclock rate of the local clock of the first zone player and the clockrate of the second zone player; and adjusting a number of audio samplesin at least a portion of the audio information for the first audio trackby an amount that corresponds to an amount of the difference between theexpected playback time and the future playback time.
 4. The first zoneplayer of claim 3, wherein determining the expected playback time of thegiven set of one or more audio samples within the audio information forthe first audio track comprises determining the expected playback timeof the given set of one or more audio samples based on a current audiosample rate of the audio information and a current audio sample playbackrate at which the first zone player is playing back the audioinformation.
 5. The first zone player of claim 1, wherein the audioinformation for the first audio track comprises a series of frames thateach include a respective portion of the audio information for the firstaudio track.
 6. The first zone player of claim 5, wherein adjusting thesample rate of at least the portion of the audio information for thefirst audio track to compensate for the difference between the clockrate of the local clock of the first zone player and the clock rate ofthe second zone player comprises: modifying at least one frame of theseries of frames to either increase or decrease a number of audiosamples played during a playback time period for the frame included inthe series of frames.
 7. The first zone player of claim 5, wherein theindicator of the first future time corresponds to a first frame in theseries of frames.
 8. The first zone player of claim 7, wherein theplayback timing information further comprises, for each subsequent framein the series of frames, an indicator of a respective future time,relative to the clock time of the local clock of the second zone player,at which the frame is to be synchronously played back by the first andsecond zone players; and wherein the first zone player further comprisesprogram instructions stored on the tangible, non-transitorycomputer-readable medium that, when executed by the at least oneprocessor, cause the first zone player to perform functions comprising:updating the respective future time for each subsequent frame to accountfor the determined differential between the clock time of the localclock of the first zone player and the clock time of the local clock ofthe second zone player.
 9. The first zone player of claim 8, whereinadjusting the sample rate of at least the portion of the audioinformation for the first audio track to compensate for the differencebetween the clock rate of the local clock of the first zone player andthe clock rate of the second zone player comprises: determining anexpected playback time of a given frame in the series of frames;comparing the expected playback time of the given frame to the updatedfuture time for the given frame and thereby determining that there is adifference between the expected playback time and the updated futuretime that is indicative of a difference between the clock rate of thelocal clock of the first zone player and the clock rate of the secondzone player; and modifying a number of audio samples in the given frameto adjust a number of audio samples played during a playback time periodfor the given frame by an amount that corresponds an amount of thedifference between the expected playback time and the updated futuretime.
 10. The first zone player of claim 9, wherein modifying the numberof audio samples in the given frame to adjust the number of audiosamples played during a playback time period for the given framecomprises: modifying the number of audio samples in the given frame toeither (a) decrease the number of audio samples played during theplayback time period for the given frame if the expected playback timeis later than the indicated future time or (b) increase the number ofaudio samples played during the playback time period for the given frameif the expected playback time is earlier than the indicated future time.11. The first zone player of claim 9, wherein determining the expectedplayback time of the given frame comprises determining the expectedplayback time of the given frame based on a current number of audiosamples included in the frame and a current audio sample playback rateat which the first zone player is playing back the audio information forthe first audio track.
 12. The first zone player of claim 1, wherein thedetermined differential between the clock time of the local clock of thefirst zone player and the clock time of the local clock of the secondzone player comprises an initial differential, and wherein the firstzone player further comprises program instructions stored on thetangible, non-transitory computer-readable medium that, when executed bythe at least one processor, cause the first zone player to perform thefollowing functions while operating as the slave zone player of thesynchrony group: after determining the initial differential between theclock time of the local clock of the first zone player and the clocktime of the second zone player, receiving, from the second zone playerover the LAN, subsequent clock information that includes a subsequentindication of the clock time of the local clock of the second zoneplayer; and based on the subsequent clock information, determining anupdated differential between the clock time of the local clock of thefirst zone player and the clock time of the local clock of the secondzone player.
 13. The first zone player of claim 12, further comprisingprogram instructions stored on the tangible, non-transitorycomputer-readable medium that, when executed by the at least oneprocessor, cause the first zone player to perform the followingfunctions while operating as the slave zone player of the synchronygroup: while still playing back the audio information for the firstaudio track, receiving, from the second zone player over the LAN, (a)audio information for a second audio track and (b) playback timinginformation associated with the received audio information for thesecond audio track that comprises an indicator of a second future time,relative to the clock time of the local clock of the second zone player,at which the first and second zone players are to begin playing back theaudio information for the second audio track; updating the second futuretime to account for the updated differential between the clock time ofthe local clock of the first zone player and the clock time of the localclock of the second zone player; and when the clock time of the localclock of the first zone player reaches the second future time, beginningto play back the audio information for the second audio track insynchrony with the second zone player.
 14. The first zone player ofclaim 1, wherein receiving the request to enter into the synchrony groupwith at least the second zone player comprises: receiving the request toenter into the synchrony group with the at least the second zone playerover the LAN from one or both of (a) a controller device that iscommunicatively coupled to the first zone player over the LAN and (b)the second zone player.
 15. The first zone player of claim 1, whereinreceiving the audio information and the playback timing information fromthe second zone player over the LAN comprises: receiving the playbacktiming information in a separate communication from the audioinformation.
 16. The first zone player of claim 1, wherein receiving theaudio information from the second zone player over the LAN comprises:receiving a first portion of the audio information from the second zoneplayer over the LAN before beginning to play back the audio informationand receiving a second portion of the audio information from the secondzone player over the LAN after beginning to play back the audioinformation.
 17. The first zone player of claim 1, further comprisingprogram instructions stored on the tangible, non-transitorycomputer-readable medium that, when executed by the at least oneprocessor, cause the first zone player to perform the followingfunctions while operating as the slave zone player of the synchronygroup: receiving, from the second zone player over the LAN, a command toterminate playback of the first audio track; and in response toreceiving the command to terminate, terminating playback of the receivedaudio information for the first audio track.
 18. The first zone playerof claim 1, wherein at least a portion of the audio information for thefirst audio track is buffered at the first zone player at the time ofreceiving the command to terminate, the first zone player furthercomprising program instructions stored on the tangible, non-transitorycomputer-readable medium that, when executed by the at least oneprocessor, cause the first zone player to perform the followingfunctions while operating as the slave zone player of the synchronygroup: in response to receiving the command to terminate, alsodiscarding any received audio information for the first audio track thatis buffered at the first zone player.
 19. Tangible, non-transitorycomputer-readable media comprising instructions encoded therein, whereinthe instructions, when executed by one or more processors, cause a firstzone player to perform a method comprising: the first zone playeroperating as a standalone zone player that is configured to play backaudio individually rather than in synchrony with another zone player,wherein the first zone player comprises a local clock that provides aclock time of the first zone player; while operating as a standalonezone player, the first zone player receiving a request to enter into asynchrony group with at least a second zone player that iscommunicatively coupled with the first zone player over a local areanetwork (LAN), wherein the second zone player comprises its ownrespective local clock that provides a respective clock time of thesecond zone player; in response to receiving the request to enter intothe synchrony group, the first zone player entering into the synchronygroup with the second zone player and transitioning from operating as astandalone zone player to operating as a slave zone player of thesynchrony group that is configured to play back audio in synchrony withthe second zone player; while operating as the slave zone player of thesynchrony group, the first zone player: receiving, from the second zoneplayer over the LAN, clock information that provides an indication ofthe clock time of the local clock of the second zone player; based onthe received clock information, determining a differential between theclock time of the local clock of the first zone player and the clocktime of the local clock of the second zone player; receiving, from thesecond zone player over the LAN, (a) audio information for at least afirst audio track and (b) playback timing information associated withthe audio information for the first audio track that comprises anindicator of a first future time, relative to the clock time of thelocal clock of the second zone player, at which the first and secondzone players are to begin playing back the audio information for thefirst audio track in synchrony; updating the first future time toaccount for the determined differential between the clock time of thelocal clock of the first zone player and the clock time of the localclock of the second zone player; adjusting a sample rate of at least aportion of the audio information for the first audio track to compensatefor a difference between a clock rate of the local clock of the firstzone player and a clock rate of the second zone player; and when theclock time of the first zone player reaches the updated first futuretime, beginning to play back the audio information for the first audiotrack in synchrony with the second zone player.
 20. The tangible,non-transitory computer-readable media of claim 19, wherein adjustingthe sample rate of at least the portion of the audio information for thefirst audio track to compensate for the difference between the clockrate of the local clock of the first zone player and the clock rate ofthe second zone player comprises: modifying at least a portion of theaudio information for the first audio track to either increase ordecrease a number of audio samples per second included in the portion ofthe audio information.
 21. The tangible, non-transitorycomputer-readable media of claim 19, wherein adjusting the sample rateof at least the portion of the audio information for the first audiotrack to compensate for the difference between the clock rate of thelocal clock of the first zone player and the clock rate of the secondzone player comprises: determining an expected playback time of a givenset of one or more audio samples within the audio information for thefirst audio track; comparing the expected playback time of the given setof one or more audio samples within the audio information for the firstaudio track to a future playback time of the given set of one or moreaudio samples as indicated by the playback timing information receivedfrom the second zone player and thereby determining that there is adifference between the expected playback time and the future playbacktime of the given set of one or more audio samples that is indicative ofthe difference between the clock rate of the local clock of the firstzone player and the clock rate of the second zone player; and adjustinga number of audio samples in at least a portion of the audio informationfor the first audio track by an amount that corresponds to an amount ofthe difference between the expected playback time and the futureplayback time.
 22. The tangible, non-transitory computer-readable mediaof claim 19, wherein the audio information for the first audio trackcomprises a series of frames that each include a respective portion ofthe audio information for the first audio track, and wherein adjustingthe sample rate of at least the portion of the audio information for thefirst audio track to compensate for the difference between the clockrate of the local clock of the first zone player and the clock rate ofthe second zone player comprises: determining an expected playback timeof a given frame in the series of frames; comparing the expectedplayback time of the given frame to an updated future time for the givenframe and thereby determining that there is a difference between theexpected playback time and the updated future time that is indicative ofa difference between the clock rate of the local clock of the first zoneplayer and the clock rate of the second zone player; and modifying anumber of audio samples in the given frame to adjust a number of audiosamples played during a playback time period for the given frame by anamount that corresponds an amount of the difference between the expectedplayback time and the updated future time.
 23. The tangible,non-transitory computer-readable media of claim 22, wherein modifyingthe number of audio samples in the given frame to adjust the number ofaudio samples played during a playback time period for the given framecomprises: modifying the number of audio samples in the given frame toeither (a) decrease the number of audio samples played during theplayback time period for the given frame if the expected playback timeis later than the indicated future time or (b) increase the number ofaudio samples played during the playback time period for the given frameif the expected playback time is earlier than the indicated future time.24. The tangible, non-transitory computer-readable media of claim 23,wherein determining the expected playback time of the given framecomprises determining the expected playback time of the given framebased on a current number of audio samples included in the frame and acurrent audio sample playback rate at which the first zone player isplaying back the audio information for the first audio track.
 25. Amethod comprising: a first zone player operating as a standalone zoneplayer that is configured to play back audio individually rather than insynchrony with another zone player, wherein the first zone playercomprises a local clock that provides a clock time of the first zoneplayer; while operating as a standalone zone player, the first zoneplayer receiving a request to enter into a synchrony group with at leasta second zone player that is communicatively coupled with the first zoneplayer over a local area network (LAN), wherein the second zone playercomprises its own respective local clock that provides a respectiveclock time of the second zone player; in response to receiving therequest to enter into the synchrony group, the first zone playerentering into the synchrony group with the second zone player andtransitioning from operating as a standalone zone player to operating asa slave zone player of the synchrony group that is configured to playback audio in synchrony with the second zone player; while operating asthe slave zone player of the synchrony group, the first zone player:receiving, from the second zone player over the LAN, clock informationthat provides an indication of the clock time of the local clock of thesecond zone player; based on the received clock information, determininga differential between the clock time of the local clock of the firstzone player and the clock time of the local clock of the second zoneplayer; receiving, from the second zone player over the LAN, (a) audioinformation for at least a first audio track and (b) playback timinginformation associated with the audio information for the first audiotrack that comprises an indicator of a first future time, relative tothe clock time of the local clock of the second zone player, at whichthe first and second zone players are to begin playing back the audioinformation for the first audio track in synchrony; updating the firstfuture time to account for the determined differential between the clocktime of the local clock of the first zone player and the clock time ofthe local clock of the second zone player; adjusting a sample rate of atleast a portion of the audio information for the first audio track tocompensate for a difference between a clock rate of the local clock ofthe first zone player and a clock rate of the second zone player; andwhen the clock time of the first zone player reaches the updated firstfuture time, beginning to play back the audio information for the firstaudio track in synchrony with the second zone player.
 26. The method ofclaim 25, wherein adjusting the sample rate of at least the portion ofthe audio information for the first audio track to compensate for thedifference between the clock rate of the local clock of the first zoneplayer and the clock rate of the second zone player comprises: modifyingat least a portion of the audio information for the first audio track toeither increase or decrease a number of audio samples per secondincluded in the portion of the audio information.
 27. The method ofclaim 25, wherein adjusting the sample rate of at least the portion ofthe audio information for the first audio track to compensate for thedifference between the clock rate of the local clock of the first zoneplayer and the clock rate of the second zone player comprises:determining an expected playback time of a given set of one or moreaudio samples within the audio information for the first audio track;comparing the expected playback time of the given set of one or moreaudio samples within the audio information for the first audio track toa future playback time of the given set of one or more audio samples asindicated by the playback timing information received from the secondzone player and thereby determining that there is a difference betweenthe expected playback time and the future playback time of the given setof one or more audio samples that is indicative of the differencebetween the clock rate of the local clock of the first zone player andthe clock rate of the second zone player; and adjusting a number ofaudio samples in at least a portion of the audio information for thefirst audio track by an amount that corresponds to an amount of thedifference between the expected playback time and the future playbacktime.
 28. The method of claim 25, wherein the audio information for thefirst audio track comprises a series of frames that each include arespective portion of the audio information for the first audio track,and wherein adjusting the sample rate of at least the portion of theaudio information for the first audio track to compensate for thedifference between the clock rate of the local clock of the first zoneplayer and the clock rate of the second zone player comprises:determining an expected playback time of a given frame in the series offrames; comparing the expected playback time of the given frame to anupdated future time for the given frame and thereby determining thatthere is a difference between the expected playback time and the updatedfuture time that is indicative of a difference between the clock rate ofthe local clock of the first zone player and the clock rate of thesecond zone player; and modifying a number of audio samples in the givenframe to adjust a number of audio samples played during a playback timeperiod for the given frame by an amount that corresponds an amount ofthe difference between the expected playback time and the updated futuretime.
 29. The method of claim 28, wherein modifying the number of audiosamples in the given frame to adjust the number of audio samples playedduring a playback time period for the given frame comprises: modifyingthe number of audio samples in the given frame to either (a) decreasethe number of audio samples played during the playback time period forthe given frame if the expected playback time is later than theindicated future time or (b) increase the number of audio samples playedduring the playback time period for the given frame if the expectedplayback time is earlier than the indicated future time.
 30. The methodof claim 29, wherein determining the expected playback time of the givenframe comprises determining the expected playback time of the givenframe based on a current number of audio samples included in the frameand a current audio sample playback rate at which the first zone playeris playing back the audio information for the first audio track.